My friend Dan Djurdjevic from Wu Wei Dao is one of the smartest martial art instructors I know. He has a blog The Way of Least Resistance, and posted on power generation Hitting Harder: Physics Made Easy. It is a good article talking about the basics of power generation. My response (which was not written very clearly at all) touched on how many instructors normally focus on muscling more power into techniques, basically through physical effort, and may not explain much in the way of how force is created for various basic techniques. Power generation in a practical application is very closely matched with strategy and tactics - and not always about juicing someone up on a straight line. Check out his article.
Hwa-rang: Calibrating Taekwondo's Short Range Roundhouse Power Generation
Taekwondo: Beginners Striking a Target
Traditional Taekwondo Technique Workshop